03/21/2014
Madden–Julian Oscillation Heating
Summary
The Madden-Julian Oscillation (MJO) is a complex multiscale coupling between the large-scale atmospheric circulation and convection in the tropics that results in pulses of clouds and precipitation moving eastward at about 5 m/s. The MJO is the primary source of tropical variability on monthly time scales and also impacts weather outside the tropics, including North American winter precipitation. Global climate models (GCMs) have difficulty in accurately simulating the MJO, possibly because of GCM failure to adequately represent atmospheric heating associated with changes in the cloud populations. U.S. Department of Energy scientists used the Community Atmosphere Model version 4 (CAM4) to examine the relative importance of heating at different altitudes to the MJO. The results show that the MJO simulation is most sensitive to the existence of heating lower in the atmosphere ahead of the center of anomalous rainfall, while excess heating higher in the atmosphere degrades the MJO signal. The study also suggests that the standard CAM4 has difficulty simulating the MJO because it produces sufficient upper-level heating but not enough lower-level heating. Given that lower atmospheric heating was most important to producing an MJO signal, these results indicate that accurate shallow convective parameterizations may be more important than deep convective ones in simulating MJO evolution in GCMs.
References
Lappen, C., and C. Schumacher. 2014. “The Role of Tilted Heating in the Evolution of the MJO,” Journal of Geophysical Research – Atmospheres 119(6), 2966–89. DOI:10.1002/2013JD020638.